The present invention relates to an electronics box for use on spacecraft such as a shuttle orbiter or space station and, more particularly, to in-orbit replaceable electronic boxes.
In general, spacecraft and space technology have developed to the point where lengthy missions are feasible and more or less permanent in-orbit stations are being developed for deployment in space. Such development presents a need for in-orbit replacement by spacesuited crew members or by robotic means, such as a robotic manipulation arm, of boxes or modules containing electronic circuit cards necessary for the functioning and control of the spacecraft. In the zero-gravity or near vacuum environment of space, it is desirable to accomplish such in-orbit replacement of the electronic boxes as rapidly as possible.
Several conventional means of fastening such boxes to mounting racks or platforms have been proposed for use on spacecraft such as multiple captive bolts shown in FIG. 1, or a keyhole arrangement with a captive fastener, shown in FIG. 2, or J-hook and captive fastener combination shown in FIG. 3.
The use of multiple captive bolts shown in FIG. 1 has the advantage providing the required intimate and high contact pressure between the box and its mounting surface. However, this fastening scheme is time consuming due to the plurality of fasteners requiring manipulation and does not led itself to ready handling by spacesuited crew members or robotic manipulator arms.
The keyhole captive fastener approach shown in FIG. 2 has the same contact pressure advantage as the multiple captive bolts of FIG. 1 plus, the additional advantage of providing a means of holding the electronics box in place during the manipulation of the captive fasteners. However, this arrangement also is not conducive to ready handling by crew members or robotic arms.
The J-hook/captive fastener arrangement shown in FIG. 3 provides the same advantages and disadvantages as the keyhole captive fastener arrangement discussed above.
Additionally, the near vacuum conditions experienced by spacecraft require that all of the heat generated by the components on the electronic circuit cards be dissipated by conduction. In some spacecraft applications, such heat is dissipated by conduction through a heat dissipating surface commonly called a coldplate, which forms the mounting surface for the electronics box. For effective heat dissipation, an intimate and high contact pressure is required at the interface between the electronics box and the coldplate.
All of the above mentioned fastening schemes are susceptible to scuffing of the coldplate as the electronics box is manipulated into position so as to align the fasteners with mating receptacles on the mounting surface. Such scuffing of the coldplate tends to degrade the heat dissipating effectiveness at the coldplate interface due to somewhat lessened contact surface at the interface.
To provide electrical or optical interconnection between the electronics box and the rest of the spacecraft, conventional electrical connectors have been proposed including pig-tailed electrical conductor cables terminating in twist-clock cylindrical connectors, partially shown at FIG. 1 and FIG. 5, available, for example, from Allied Amphenol Products of Oak Brook, Ill.
The twist-lock cylindrical connectors provide for positive and secure interconnections. However, such connectors are not rapidly manipulated by spacesuited crewmembers due to the rotational movement required and, if the electronics box is provided with a plurality of such connectors, the disconnection and reconnection of each connector becomes a time consuming process.
Two other problems are addressed by the instant invention involving, firstly, the heat conduction path within the electronics box from the circuit cards to the coldplate interface and secondly, the internal routing of electrical wires or cables from the circuit card connectors mounted in the motherboard to the cylindrical electrical connectors used for external connection of the electronics box.
Heat conduction path within conventional electronics boxes for spacecraft are arranged as shown in FIG. 4. Each circuit card is provided with a thermal plane formed of an efficient heat conductor such as copper which provides a heat sink for the electronic components mounted on the circuit card. The thermal plane is coextensive with the peripheral edges of the circuit card.
The circuit cards are mounted in individual card edge guides formed in the outer walls of the box. The circuit card is usually inserted into a receptacle in a motherboard which is positioned between the circuit card and the bottom of the box. The circuit card thermal plane is held in intimate heat conducting contact with the edge guides which, in turn, carry the heat to electronics box coldplate interface formed on the bottom surface of the box. However, with the motherboard interposed between the circuit card and the bottom mounting surface of the box, the only heat transfer occurs along the sidewall edge guides. In this arrangement, heat from the upper portion of the circuit card must be conducted the full height of the circuit guide before it can be transferred to the coldplate interface.
Electrical connection between the cylindrical connectors mounted on the endwall of the electronics box, shown in FIG. 5, is accomplished by means of pig-tail harness cable or flex cable (not shown) connections at both the circuit card receptacle on the motherboard and the external cylindrical electrical connections. As can be seen in FIG. 5, the sequential routing of the cables or flex circuit cables (not shown) to the external cylindrical connectors from the furthest circuit cards to the nearest circuit cards leads to an inefficient use of the internal volume of the box resulting in the necessity of providing a larger electronics box with sufficient volume to accommodate the necessary cable routings.
An object of the present invention is to provide an electronics box that permits rapid manual or robotic in-orbit replacement of the electronic box.
Another object of the present invention is to provide an electronics box that permits in-orbit removal and replacement of the electronics box without scuffing the coldplate or coldplate interface surface.
Another object of the present invention is to provide the electronics box with a fastening means for rapidly securing the box to its mounting surface.
Another object of the present invention is to provide the electronics box with a short path internal cable routing between the circuit card receptacle on the motherboard and the external electronics box connector.
Another object of the present invention is to provide the electronics box with a short direct internal heat conducting path between the circuit card thermal plane and the box coldplate interface.
Another object of the present invention is to provide in-line connectors which require a straight-line motion to mate as the box is drawn down against its mounting surface.
The electronics box contemplated by this invention includes a cover and a bottomwall spaced from the cover by opposed sidewalls of the box. A motherboard having circuit card connectors is mounted in the box adjacent to the cover. The box further includes in-line connectors mounted adjacent to the motherboard with the in-line connectors interconnected with the circuit card connectors mounted on the motherboard. Further advantages and details of our invention can be had from the following description and claims taken together with the accompanying drawing.